Polyamino acid derivatives, particularly polyaspartic acid, have aroused interest very recently because of their properties. One advantage of the polyaspartic acid skeleton is its very good environmental compatibility and biological degradability. The biological degradability of polymeric aspartic acids is a result of the basic structure, which is similar to a natural one and which has been derived from polyamino acids. The advantageous properties of polyaspartic acids with respect to the biological degradability in comparison to polymers with C-C skeletons (for example, polyacrylates) have been described (Abstracts of papers of the ACS, 1994, V208, 423-4; M. B. Freeman, Y. H. Paik, G. Swift, R. Wilczynski, S. K. Wolk, K. M. Yocom). The applications proposed are, primarily, use as biologically degradable complexing agents, softeners and detergent builders.
The immediate synthetic precursor in most cases is polysuccinimide, the cyclic imide of polyaspartic acid, or derivatives of monoethylenically unsaturated carboxylic acids, such as maleic acid.
EP-A-0578449 describes the synthesis of polysuccinimide by the heating of aspartic acid in polyalkylene glycols, alone or in a mixture with additional amino acids. WO 92/14753 describes the synthesis of polysuccinimide and polyaspartic acid by the thermal condensation of aspartic acid. U.S. Pat. No. 5,219,952 describes the synthesis of polysuccinimide from maleic acid anhydride and ammonia, and the hydrolysis of the product to form polyaspartic acid. EP-A-0578448 describes the synthesis of polysuccinimide by the heating of amino acids and monoethylenically unsaturated dicarboxylic acids or their ammonium salts.
These compounds present numerous advantageous properties, but they have no surface active properties. In order to obtain compounds which combine the positive properties of polyaspartic acid with surfactant properties, it is necessary to introduce hydrophobic, oil-compatible molecule parts into the predominantly hydrophilic polyaspartic acid skeleton.
The reaction of polysuccinimide with amines to form polyaspartic acid amides is also known in the state of the art (for example, DE-A-2253190). U.S. Pat. No. 5,292,858 describes the synthesis of copolymeric polyamino acid amides by the hydrolysis of polysuccinimide derivatives, prepared by reacting maleic acid semiesters with ammonia or amines.
In accordance with these teachings, copolymers with free carboxylic acid groups and alkylamide groups can be prepared. These copolymers however present serious drawbacks. Thus, as a result of the preparation, the products contain more or less small amounts of free alkylamines, which are undesired in many applications and whose use can also entail toxicological and ecological drawbacks. The alkylamines can additionally be released, for example, by hydrolytic cleavage, during the use of such copolymers.